How do I import garment patterns into blender?
You need to export the patterns form the app you are using on some format that is supported by blender.

Image

JPEG, JPEG2000, PNG, TARGA, OpenEXR, DPX, Cineon, Radiance HDR, SGI Iris, TIFF

Video

AVI, MPEG and Quicktime.

3D

Alembic, 3D Studio (3DS), COLLADA (DAE), Filmbox (FBX), Autodesk (DXF), Wavefront (OBJ), DirectX (x), Lightwave (LWO), Motion Capture (BVH), SVG, Stanford PLY, STL, VRML, VRML97, X3D.